A compound represented by the formula (I):
[wherein R1 represents a C1-C19 alkyl group and R2 represents a C1-C4 alkyl group] or a pharmacologically, acceptable salt thereof is known to have excellent neuraminidase inhibitory activity and therefore to be useful as a drug for treatment or prevention of influenza (Patent Document 1 or 2).
A trifluoroacetic acid salt of a compound represented by the formula (III):
is known to have excellent neuraminidase inhibitory activity and therefore to be useful as a drug for treatment or prevention of influenza (Non-patent Document 1 or 2).
Process W is known as a method for manufacturing a compound represented by the formula (Ia), which is embraced in a compound represented by the formula (I) or a pharmacologically acceptable salt thereof, [hereinafter also referred to as “compound (Ia)”; the same shall be applied with respect to other formulas] (Patent Document 1). In Process W, n-Hep represents a 1-heptyl group.

Process X is known as a method for manufacturing compound (Ib), which is embraced in compound (I) or a pharmacologically acceptable salt thereof (Patent Document 2). Compound (IVk) is a synthetic intermediate in Process W. In Process X, n-Hep represents a 1-heptyl group.

Process Y is known as a method for manufacturing compound (IIIa), which is a trifluoroacetic acid salt of compound (III) (Non-patent Document 1). The procedures from compound (IVc) to compound (IVe) and from compound (IVf) to compound (IVh) in Process Y are the same as in Process W.

Process Z is known as a method for manufacturing compound (IIIa), which is a trifluoroacetic acid salt of compound (III) (Non-patent Document 2). In Process Z, the procedure from compound (IVf) to compound (IVh) is the same as in Process W, and the procedure from compound (IVh) to compound (IIIa) is the same as in Process Y.

From the viewpoint of industrial production, the aforementioned Process W, Process Y, or Process Z could be improved in points such as the following:
[Process W]
    (1) the overall yield is low since a procedure with a low yield is included [overall yield of compound (Ia): 0.2%];    (2) N-methylation of an acetamide group occurs as a side reaction of methylation reaction of a hydroxy group [production procedure of compound (IVb)];    (3) an inefficient enzyme reaction is included [production procedure of compound (IVd)];    (4) a hazardous azidation reaction at high temperature is included [production procedure of compound (IVg)]; or    (5) in the acylation reaction, (a) protection of a carboxyl group is necessary, (b) 2,3-diacylated product is generated as by-product, and (c) purification by silica gel column chromatography is necessary to remove octanoic acid derived from the reagent [production procedure of compound (IVk)];[Process Y]    (1) the overall yield is low since a procedure with a low yield is included [yield of compound (Va): 34%, overall yield from compound (Va) to compound (IIIa): 10 to 23%, resulting in 3 to 8%];    (2) an inefficient enzyme reaction is included [production procedure of compound (IVd)]; or    (3) a hazardous azidation reaction at high temperature is included [production procedure of compound (IVg)];[Process Z]    (1) the overall yield is low since a procedure with a low yield is included [yield of compound (VIa): 35%, overall yield from compound (VIa) to compound (IIIa): 1 to 33%, resulting in 0.4 to 12%];    (2) an expensive silyl protective group is used;    (3) N-methylation of an acetamide group occurs as a side reaction of the methylation reaction of a hydroxy group [production procedure of compound (IVb)]; or    (4) a hazardous azidation reaction at high temperature is included [production procedure of compound (IVg)].
[Patent Document 1] U.S. Pat. No. 6,340,702 (corresponding to Japanese Patent No. 3209946)
[Patent Document 2] U.S. Pat. No. 6,844,363 (corresponding to Japanese Patent Application No. 2002-012590)
[Non-patent Document 1] T. Honda et al., Bioorganic Medicinal Chemistry Letters, 2002, pp. 1921-1924
[Non-patent Document 2] T. Honda et al., Bioorganic Medicinal Chemistry Letters, 2002, pp. 1925-1928
As a result of conducting extensive studies on methods for manufacturing neuraminic acid derivatives, the inventors of the present invention have found a novel method for manufacturing neuraminic acid derivatives via novel synthetic intermediates of the present invention that is superior to publicly known manufacturing methods from an industrial perspective, and have found that neuraminic acid derivatives with high purity can be obtained in high yield by the manufacturing method. The present invention has been completed based on the aforementioned findings.